A towel was used for drying or covering a person's body.
In 1894, Sam Jones provided Emmeline and Nathaniel Seers with towels after she helped them escape Zygons. (PROSE: The Bodysnatchers)
Jack Harkness asked Neil Redmond for a towel after he was soaked in the rain. (AUDIO: Uncanny Valley)
Yvonne Hartman was left wearing nothing but a towel after the Manor Rest Hotel burnt down. (AUDIO: One Rule)
Roz Forrester had a towel in the TARDIS bathroom. Chris Cwej used it after she died. (PROSE: Lungbarrow)